Replace get*PhoneAccounts* public API methods with new method (1/3)

Hide getCallCapablePhoneAccounts and getPhoneAccountsSupportingScheme
because a third party app should not be able to see all phone accounts
registered. Replace instead with getPhoneAccountsForPackage(Context)
which will only return the phone accounts registered by a particular package.

Bug: 17510811
Change-Id: I8465ef4f13b62fe83f51835cfffe1656298041a8